Improvements in and relating to displays

ABSTRACT

A display apparatus is described that comprises an optical ocular part ( 3 ) arranged for viewing a scene therethrough, and a waveguide display part ( 6 ) arranged for guiding image-bearing light to a transparent display output area ( 16 ) thereof and thereat displaying the image. The ocular part and/or the waveguide display part are positioned, or are arranged to be positioned, mutually in register for viewing simultaneously the scene with the displayed image incorporated in it, through the transparent display output area. A focuser part ( 17 ) positioned in register with the display output area focuses simultaneously the scene and the incorporated image for focussed viewing by a user ( 13 ).

The present invention relates to displays, and particularly, though notexclusively, to head-up displays such as head-mounted displays and thelike.

Head-mounted displays may employ transparent waveguide displays designedto generate an image via a transparent display screen through which anexternal scene is viewed by the helmet wearer (e.g. the view from acockpit of an aircraft). The image thereby forms an overlay to theviewed scene and may comprise flight information (speed, altitude,positional information etc.). When it is necessary to employ additionaloptical aids, such as monocular or binocular elements in the form ofnight-vision viewers/goggles (NVG) or the like, a focal mismatch mayarise between the optical output of the waveguide display and theadditional optical aid. In particular, the user of a night-vision viewerinvariable will wish to set the focus of the NVG in the region of −1.0Dioptres. This may lead to a loss in conformal display accuracy at thewaveguide exit pupil and will cause user discomfort.

The invention seeks to address these matters.

In a first aspect, the invention may provide a display apparatuscomprising: an optical ocular part arranged for viewing a scenetherethrough; a waveguide display part arranged for guidingimage-bearing light to a transparent display output area thereof andthereat displaying the image; wherein the ocular part and/or thewaveguide display part are positioned or are arranged to be positionedmutually in register with one another for viewing simultaneously thescene with the displayed image incorporated therein through thetransparent display output area; and, a focuser part positioned inregister with the display output area for focussing simultaneously thescene and the incorporated image for focussed viewing by a user. In thisway, the focuser may apply a desired focussing of the combined light ofthe guided image from the waveguide display part and the light of thescene viewed through the ocular part. The ocular part may be adjustableto adjust the focus thereof (e.g. in the range from about −1.0 Dioptresto about +6 Dioptres).

The waveguide display part may comprise a planar waveguide display. Theocular part may be comprised within a monocular lens assembly which iseither a lone lens assembly or forms one lens assembly within abinocular lens assembly.

The waveguide display part may be arranged to output the image-bearinglight at the display output area as collimated light. The ocular partmay be arranged or may be adjustable to output to the display outputarea collimated light conveying the scene. The optical output of theocular part and of the waveguide display part may each comprisecollimated light. The focuser part may thus be arranged to apply afocussing to the collimated combined light of both the ocular part andthe waveguide display part.

The focuser part may be arranged or operable to possess a negativeoptical power thereby to diverge light received thereby from the displayoutput area. For example, focuser part may be arranged to provide anoptical power in the range from about 0 (zero) Dioptres to about −2Dioptres, or more preferably between −0.5 Dioptres to about −1.5Dioptres, e.g. about −1.0 Dioptres.

The focuser part may be switchable between a first state in which itpossesses substantially no optical power and a second state in which itpossesses an optical power for focussing light received thereby from thedisplay output area.

The ocular part may be moveably connected to the waveguide display partand is moveable between a first position in which it is not in saidregister with the waveguide display part and a second position in whichit is so in register.

The focuser part is preferably arranged to switch from the first stateto the second state when the ocular part is moved from the firstposition into the second position. The focuser part may be arranged toswitch from the second state to the first state when the ocular part ismoved from the second position into the first position.

In a second of its aspects, the invention may provide a method ofdisplaying a scene comprising: providing an optical ocular part andviewing a scene therethrough; providing a waveguide display part andguiding image-bearing light to a transparent display output area thereofand thereat displaying the image; positioning the ocular part and thewaveguide display part mutually in register with one another and viewingsimultaneously the scene with the displayed image incorporated thereinthrough the transparent display output area; and, providing a focuserpart positioned in register with the display output area and therewithfocussing simultaneously the scene and the incorporated image-bearinglight for focussed viewing by a user.

The method may include outputting from the waveguide display part theimage-bearing light as collimated light at the display output area, andoutputting to the display output area collimated light from the ocularpart conveying the scene.

According to the method the focuser part may be arranged or be operableto possess a negative optical power, the method may include diverginglight received thereby from the display output area.

The focuser part is preferably switchable between a first state in whichit possesses substantially no optical power and a second state in whichit possesses an optical power for focussing light received thereby fromthe display output area. The ocular part may be moveably connected tothe waveguide display part and is preferably moveable between a firstposition in which it is not in said register with the waveguide displaypart and a second position in which it is so in register.

The method may include switching the focuser part from the first stateto the second state by moving the ocular part from the first positioninto the second position.

The method may include switching the focuser part from the second stateto the first state by moving the ocular part from the second positioninto the first position.

The focuser part may be arranged or be operable (e.g. switchable) topossess a negative optical power thereby to diverge light receivedthereby from the display output area.

An illustrative but non-limiting example of the invention shall now bedescribed with reference to the accompanying drawings of which:

FIG. 1 is a schematic view of a helmet-mounted display apparatusaccording to the invention, comprising a pair of night-vision goggles(NVG) attached to a helmet and positioned in a stowed position;

FIG. 2 is a schematic view of a helmet-mounted display apparatusaccording to the invention, comprising a pair of night-vision goggles(NVG) attached to a helmet and positioned in a deployed position topermit viewing of a scene therethrough by a user;

FIG. 3 schematically illustrates a slab waveguide display;

FIGS. 4A and 4B show two switched states of a switchable holographicBragg grating unit;

FIG. 5 shows a binocular night vision goggles (NVG) according to anembodiment the invention.

In the drawings, like articles are assigned like reference symbols.

Referring to FIG. 1, there is shown a helmet mounted display apparatuscomprising an optical ocular part (1, 2, 3) which is one of two separateand parallel monocular components of a pair of binoculars of anight-vision goggle (NVG) unit. The NVGs are arranged for viewing anight-time scene therethrough and include an objective lens part (2)optically coupled to an eyepiece lens part (3) via an image intensifierpart (1) arranged to intensify an image of a scene formed by theobjective lens part for viewing via the eyepiece part. The NVGs may besuch as would be readily available and/or apparent to the skilledperson.

The display apparatus includes a planar waveguide display part (6)comprising an image generator part (7) for generating image-bearinglight, and a planar waveguide upon or within which is formed two or morediffraction gratings (e.g. Bragg gratings). The image generator part isin communication with an image controller part (8) arranged to generateimage data (digital or analogue) and to control the image generator partaccording to the image data to generate an image accordingly fordisplay.

A first such diffraction grating defines a waveguide input region forreceiving image-bearing light from the image generator part (7) and fordiffracting image-bearing light into the planar (e.g. slab) waveguidefor guiding therealong to a transparent display output area thereof andthereat displaying the image. A second such diffraction grating locatedat the output area is arranged to diffract out of the waveguide theguided image-bearing light from the waveguide input region.

The eyepiece part (3) and the waveguide display part are shownpositioned (and are arranged to be moveably positioned) mutually inregister for the viewing simultaneously an external night-time scenesuch that a display image from the image generator part is incorporatedin the scene through the transparent display output area of thewaveguide part (6).

A switchable holographic lens part (9) is positioned in register withthe display output area of the waveguide part (6) for focussingsimultaneously the night-time scene produced by the NVG (1, 2, 3) andthe incorporated image-bearing light for focussed viewing by a user.(13).

The waveguide display part is arranged to output the image-bearing lightat the display output area as collimated light. The eyepiece part (3) ofthe ocular part is arranged to be adjustable in optical power to enablea user to control the focus of the scene-bearing light output thereby.When used in isolation, a typical pair of NVGs would be arranged with aneyepiece of negative optical power set to diverge the scene-bearinglight output thereby to achieve a close focus for use by a user/wearerof the NVGs. However, this conflicts with the collimating output power(e.g. substantially/effectively zero, or negligibly small optical power)of the planar waveguide which does not bring image-bearing light to aclose focus. When the waveguide part and the NVG ocular part are usedtogether, as shown in FIG. 2, the state of focus of scene-bearing lightand the state of focus of the image-bearing light is adjusted to renderthem consistent and optimal. This avoids the visual discomfort a userwill otherwise suffer and permits the display apparatus to display botha night-time scene and the image conveyed by the waveguide partconcurrently (the latter overlaid on the former) at the display outputarea of the waveguide part via collimated light conveying both thenight-time scene and the guided image from the image generator part (7).

The switchable holographic lens comprises an electrically switchabletransmissive Bragg grating formed on a transparent substrate. It isstructured to define a holographic optical lens which has a negativeoptical power (e.g. −1.0 Dioptres) when activated electrically, and haseffectively/substantially no optical power when not electricallyactivated (e.g. effectively zero Dioptres). When activated, theholographic lens is thereby arranged to diverge light received therebyfrom the display output area to bring it to a close focus desired by auser. The light so focussed is received by the holographic lens ascollimated light conveying both the night-time scene from the NVGs andthe image-bearing light originating from the image generator part (7).

The focuser part may be switchable according to a switch control unit(10) between a first state shown in FIG. 1 in which it possessessubstantially no optical power and a second state shown in FIG. 2 inwhich it possesses an optical power for focussing light received therebyfrom the display output area.

The ocular part of the NVGs is moveably connected via a pivotableconnection arm (4) to a helmet (5) to which the waveguide display partis connected or fixed. The ocular part is (e.g. pivotingly) moveablerelative to the helmet between a first “stowed” position (FIG. 1) inwhich it is not in register with the waveguide display part and a second“deployed” position (FIG. 2) in which it is so in register.

The control unit is arranged to control the focuser part to switch fromthe first state to the second state when the ocular part is moved fromthe stowed position into the deployed position, and similarly, to switchfrom the second state to the first state when the ocular part is movedfrom the deployed position into the stowed position. In this way, withthe holographic lens part switched “off” (i.e. no lens) the opticalwaveguide part is able to be used when the NVGs are in the stowedposition and the user's eyes naturally focus to receive collimatedimage-bearing light from the waveguide part when viewing the environmentthrough the display area of the waveguide part—e.g. during the daytime.Conversely, when it is desired to use the NVGs while still using thewaveguide display part, the holographic lens is switched on and theeyepiece of the NVG ocular set to collimate its output. This enables thelight output of both the ocular and the waveguide part to be suitablyclose-focussed by the holographic lens with optimal comfort for theuser. In effect, the holographic lens serves the function which isusually served by the eyepiece of the NVG ocular, while allowing theimage conveyed by the waveguide to be comfortably incorporated into theoverall scene viewed by the user (13).

FIG. 3 shows schematically an optical waveguide suitable for thewaveguide display part (6). The optical waveguide is a slab waveguidecomprising a first (input) diffractive grating region (14) arranged toreceive image-bearing light from the image generator part (7) and todiffract the received light along the optical waveguide by totalinternal reflection between the planar surfaces of the slab waveguide.An intermediate diffraction grating (15) is optically coupled to thefirst diffractive grating region by the optical waveguide to receive thediffracted light from the first grating and to expand the received lightin a lateral dimension by diffraction as shown by arrows (15A). A second(output) diffractive grating region (16) is optically coupled to theintermediate diffraction grating by the optical waveguide to receive theexpanded light and to output the received expanded light from theoptical waveguide by diffraction thereby to display the image conveyedby the image-bearing light when input at the first (input) diffractiongrating (14).

The image projector part (7) may be a micro-display pico-projector, suchas would be readily available to the skilled person. For example, thepico-projector may include an illumination source (if required), amicro-display area, and one of more lenses and optical componentsarranged to collimate an image from the micri-display area and inject itinto the waveguide. For example, the micro-display may be a reflectiveLCoS (Liquid crystal on silicon) device, which is a micro-projection ormicro-display technology well known in the art. Alternatively, themicro-display may be DMD (digital micro-mirror device) also well knownin the art, which may comprise a chip having on its surface manymicroscopic mirrors arranged in an array which correspond to the pixelsin an image to be displayed. The mirrors can be individually rotated toan on or off state to collectively generate an image to be displayed viareflected light.

FIGS. 4A and 4B schematically show the switchable holographic lens unitin an un-activated state (“off”) in which no holographic lens is present(FIG. 4A) and also in an activated state (“on”) in which a holographiclens is generated. The unit comprises an electrically switchabletransmissive Bragg grating (17) formed on a transparent substrate (9) ofplastic or glass of other suitable optically transmissive material suchas would be readily apparent to the skilled person. The switchabletransmissive Bragg grating may comprise a Bragg grating recorded intoliquid crystal such as is known in the art. An example of this isdescribed in “Electro-optic properties of switchable gratings made ofpolymer and nematic liquid-crystal slices” by A. d'Alessandro et al.:Jun. 15, 2004/Vol. 29, No. 12/OPTICS LETTERS. An alternative is to use aliquid crystal switchable lens such as is described in EP0693188B1.

It is structured to define a holographic optical lens which has anegative optical power (e.g. −1.0 Dioptres) when activated electricallyby application of electrical voltage to cause the distribution ofrefractive index across the surface of the unit (9) to vary in such away as to define the Bragg grating. Removal of the electrical voltageremoves the pattern of refractive index and causes the Bragg grating todisappear.

Thus, when no electrical voltage is applied the unit haseffectively/substantially no optical power (e.g. effectively zeroDioptres). When activated, the holographic lens is thereby generated andis arranged to diverge light received thereby from the display outputarea (16) of the optical waveguide part (6) to bring it to a close focusdesired by a user, as shown in FIG. 4B.

The switch control unit (10) is arranged to selectively apply/remove therequired voltage to the switchable Bragg grating unit (9) to cause it toswitch between the first state shown in FIGS. 1 and 4A in which itpossesses substantially no optical power and the second state shown inFIGS. 2 and 4B in which it possesses negative optical power. The switchcontrol unit (10) may, in preferred embodiments be connected to anexternal switch element (20) formed in the pivotable connection arm (oralternatively in the helmet 5) which is arranged to adopt automaticallya first switch state when the NVGs are in the stowed position (FIG. 1)and to adopt automatically a second state when the NVGs are in thedeployed position (FIG. 2). The switch control unit (10) is arranged, insuch embodiments, to be responsive to the external switch element whenin the first state to not activate the switchable Bragg grating, and tobe responsive to the external switch element when in the second state toactivate the switchable Bragg grating. In this way, the switchable Bragggrating may be automatically activated when the NVGs are deployed. Inother embodiments, the external switch unit may be simply ahand-operated switch operable directly (manually) by the user.

The setting of the focus of an ocular of the NVGs may be performedmanually by the wearer by adjustment of the eyepiece(s) thereof. Anappropriate eyepiece may thus be manually adjusted to collimate by thewearer.

FIG. 5 shows schematically how a pair of NVG oculars may be used withthe waveguide display part and the focuser part of the invention in apreferred embodiment. Only one of the two oculars is arranged incombination with a waveguide display part (6) and focuser part (9). Thatocular (13) is arranged to output collimated light from a viewed scene,whereas the other ocular (1B, 2B, 3B) of the pair is arranged to outputdivergent light close-focussed via eyepiece (3B) optical elementspossessing negative optical power (e.g. about −1.0 Dioptres). Thenegative optical power of that other ocular (3B) is substantiallymatched by the negative optical poser of the focuser unit (9) with theresult that the user sees a given scene through both eyes (13 and 13B)appropriately focussed with an image from an image generation unit (7)superimposed thereupon in the view through one eye (13).

As can be observed from FIGS. 1, 2 and 5, the planar waveguide displaypart (6) and the switchable holographic lens part (9) are arranged inthe field of view of a user (13) such that the user (13) will view thescene and information generated by the image controller part (8)superimposed upon the view of the scene. Furthermore, the planarwaveguide display part (6) and the switchable holographic lens part (9)are arrange such that the optical ocular part (1, 2, 3), which is one oftwo separate and parallel monocular components of a pair of binocularsof a night-vision goggle (NVG) unit, can be moved between stowed anddeployed position such that the planar waveguide display part (6) andthe switchable holographic lens part (9) are positioned between the eyeof the user and the optical ocular part (1, 2, 3). This means that whenthe optical ocular part (1, 2, 3) is in the stowed position (FIG. 1) theplanar waveguide display part (6) can provide symbology or imagery tooverlay the forward scene and when the optical ocular part (1, 2, 3) ismoved to the deployed position (FIG. 2) the planar waveguide displaypart (6) and the switchable holographic lens part (9) do not interferewith deployment whilst being able to provide symbology or imagery tooverlay the enhanced night vision forward scene. Accordingly, thisallows the image bearing light to be generated between the user's eyeand an image intensifier of the ocular part (1, 2, 3).

The embodiments described above are intended as non-limited examples ofthe invention the scope of which is intended to encompass variants,modifications and equivalents to the examples such as would be readilyapparent to the skilled person.

1-15. (canceled)
 16. A display apparatus comprising: an optical ocularpart for viewing a scene therethrough; and a waveguide display partarranged for guiding image-bearing light from an image generator part toa transparent display output area of the waveguide display part suchthat the image-bearing light is viewable combined with light from thescene passing through the transparent display output area, wherein atleast one of the ocular part and the waveguide display part is moveablerelative to the other between a stowed relative position and a relativeposition of alignment such that when in the relative position ofalignment, light from the scene viewable through the ocular part isarranged to pass through the transparent display output area and to beviewable combined with the image-bearing light, the display apparatusfurther comprising a switchable focuser part positioned in alignmentwith the display output area for focusing simultaneously light from thescene viewable through the ocular part, when the waveguide display partand the ocular part are in the relative position of alignment, combinedwith the image-bearing light for focused viewing by a user, wherein thestate of focus of the light from the scene after passing through theoptical ocular part is consistent with the state of focus of theimage-bearing light.
 17. The display apparatus according to claim 16, inwhich the image-bearing light is collimated and the ocular part isarranged or is adjustable to output to the display output areacollimated light from the scene.
 18. The display apparatus according toclaim 16, in which the focuser part is arranged or operable to possess anegative optical power thereby to diverge light received from thedisplay output area.
 19. The display apparatus according to claim 16, inwhich the focuser part is switchable between a first state in which itpossesses substantially no optical power and a second state in which itpossesses an optical power for focusing light received from the displayoutput area.
 20. The display apparatus according to claim 19, in whichthe ocular part is moveably connected to the waveguide display part andis moveable between a first position in which it is in the stowedrelative position with respect to the waveguide display part and asecond position in which it is in the relative position of alignmentwith respect to the waveguide display part.
 21. The display apparatusaccording to claim 20, in which the focuser part is arranged to switchfrom said first state to said second state when the ocular part is movedfrom said first position into said second position.
 22. The displayapparatus according to claim 20, in which the focuser part is arrangedto switch from said second state to said first state when the ocularpart is moved from said second position into said first position. 23.The display apparatus according to claim 20, further comprising a switchelement arranged to detect a change in relative position of the ocularpart and the waveguide display part from the first position to thesecond position and from the second position to the first positionthereby to switch the focuser part from the first state to the secondstate and from the second state to the first state, respectively. 24.The display apparatus according to claim 16, in which the waveguidedisplay part comprises a planar waveguide display.
 25. The displayapparatus according to claim 16, in which the ocular part is comprisedwithin a monocular lens assembly.
 26. The display apparatus according toclaim 16, in which the ocular part is comprised within one lens assemblywithin a binocular lens assembly.
 27. The display apparatus according toclaim 26, wherein each lens assembly of the binocular lens assemblyincludes an independently adjustable eyepiece lens such that theeyepiece lens of the assembly comprising the ocular part may beindependently adjusted such that the state of focus of the light fromthe scene after passing through the ocular part is consistent with thestate of focus of the image-bearing light.
 28. The display apparatusaccording to claim 27, wherein the eyepiece of the lens assemblycomprising the ocular part is arranged to output collimated light fromthe scene and the eyepiece of the other lens assembly of the binocularlens assembly is arranged to output focused light from the scene, suchthat the optical power of the eyepiece of the other lens assembly issubstantially matched by the optical power of the focuser part whenswitched to said second state.
 29. The display apparatus according toclaim 26, in which the ocular part is comprised in a lens assembly of anight vision goggle system.
 30. The display apparatus according to claim15, in which the switchable focuser part comprises a switchabletransmissive Bragg grating.